Evaporation assembly with vapor circulating means

ABSTRACT

An evaporation assembly for concentrating liquids having an evaporation area for conveying a liquid to be concentrated and a heating system for heating and concentrating the liquid conveyed through the evaporation area. The evaporation area includes a liquid inlet for introducing liquid to be concentrated into the evaporation area, and a liquid and vapor outlet for conveying the liquid through the evaporation area. A vapor circulating system is coupled between the liquid inlet end and the liquid and vapor outlet of the evaporation area for increasing the velocity of the liquid to be concentrated for inpeding or removing precipitated particles or deposits from the heat exchange surfaces.

FIELD OF THE INVENTION

The present invention relates to an evaporation assembly forconcentrating liquids. More particularly, the present invention providesan evaporation assembly for impeding or removing solid deposits from theheat exchange surfaces. Vapors are circulating from the evaporation areainto the inlet liquid for increasing the velocity of the mixture of theliquid and vapors being conveyed through the evaporation area, and thusimpeding the precipitation of particles or deposits on the heat exchangesurfaces.

BACKGROUND OF THE INVENTION

Two typical types of evaporation devices are the falling film type andthe rising film type. In the falling film type, the liquid is forceddownwardly along essentially vertical heat transfer walls with steam orvapors being generated between liquid films. On the other hand, in therising film type, the liquid is forced upwardly along essentiallyvertical heat transfer walls with steam or vapors being generatedbetween liquid films. In the falling film type as well as the risingfilm type of evaporation devices, the vertical heat transfer walls maybe vertically extending plates or tubes with a hot medium, such assteam, circulating between the heat transfer walls.

Examples of falling film type evaporation devices utilizing tubes aredisclosed in U.S. Pat. Nos. 4,076,576 to Marttala and 4,641,706 toHaynie, which are both incorporated herein by reference. An example ofan evaporation device utilizing vertically extending heat exchangeplates is disclosed in U.S. Pat. No. 4,586,565 to Hallstrom et al, whichis incorporated herein by reference.

A major problem occurring in most evaporation assemblies is thecollection of solid deposits on the heat exchange surfaces. Inparticular, when the liquid in the tubes or evaporation area begins toevaporate and the solubility coefficient is surpassed, crystals or gumsstart to precipitate. Accordingly, the greater the concentration of theliquid, the greater is the viscosity of the liquid as well. Accordingly,the concentrated liquid tends to move slower, and consequently eitherthe precipitate salt crystals or the gums from the liquid will begin toadhere or stick to the walls of the heat exchange surfaces. Once thecrystals or gums begin to adhere to the hot wall of the heat exchanger,additional crystals or gums will begin to adhere at an exponential rate.

These solid deposits or scalings decrease the overall efficiency of theheat exchange by reducing the overall heat exchange coefficient, i.e.,the amount of heat exchange per unit of time over a given surface area.Moreover, the solid deposits can, over a period of time, build up on theheat exchange surfaces to a point requiring stopping operation andcleaning the heat exchange surfaces. Accordingly, this is a very seriousproblem which designers or manufacturers have made many efforts toovercome.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide anevaporation assembly that circulates vapors formed from concentratingthe liquid into the evaporation area at a sufficient velocity to impedethe precipitated particles from adhering or sticking to the walls of theheat exchanger.

Another object of the present invention is to provide an evaporationassembly that continuously impedes solid deposits from sticking onto thewalls of the heat exchanger without stopping operation of theevaporation assembly.

A further object of the present invention is to provide an evaporationassembly that has a higher heat transfer coefficient than similarevaporation assemblies with identical heat exchange surfaces.

The foregoing objects are basically attained by an evaporation assemblyfor concentrating liquids, comprising an evaporation area, with a liquidinlet coupled to one end of the evaporation area for conveying liquid tobe concentrated into the evaporation area and a liquid and vapor outletcoupled to the other end of the evaporation area for removing andseparating concentrated liquid and vapors from the evaporation area. Aheating medium is positioned adjacent the evaporation area for heatingthe liquid conveyed through the evaporation area. Vapor circulatingmembers are coupled to the liquid and vapor outlet and the liquid inletfor conveying vapors from the liquid and vapor outlet to said liquidinlet and for mixing vapors from the liquid and vapor outlet with liquidto increase the velocity of the mixture of the liquid and vaporsconveyed through the evaporation area.

The foregoing objects are further attained by a method for concentratingliquids, comprising the steps of conveying liquid through an evaporationarea from an inlet end to an outlet end; heating the liquid conveyedthrough the evaporation area to concentrate the liquid; circulatingvapors generated by concentrating the liquid in the evaporation areafrom the outlet end of the evaporation area to the inlet end of theevaporation area for mixing with liquid in the inlet end to increasevelocity of liquid conveyed through the evaporation area; and collectingthe concentrated liquid at the outlet end.

Other objects, advantages and salient features of the invention willbecome apparent from the following detailed description, which, taken inconjunction with the annexed drawings discloses preferred embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the drawings which form a part of this disclosure:

FIG. 1 is a partial side elevational view of an evaporation assembly inaccordance with a first embodiment of the present invention;

FIG. 2 is a schematic perspective view of the evaporation assembly ofFIG. 1 with the heat exchange tubes removed for clarity;

FIG. 3 is a top plan view in section taken along line 3--3 of FIG. 1;

FIG. 4 is a partial side elevational view of an evaporation assembly inaccordance with a second embodiment of the present invention; and

FIG. 5 is a partial side elevational view of an evaporation assembly inaccordance with a third embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring initially to FIG. 1, an evaporation assembly 10 is illustratedin accordance with the present invention, and includes an outer housing12 with an inlet or head portion 14 at its upper end for receiving inletliquid to be concentrated, a heat exchange portion 16 below inletportion 14 for concentrating the liquid being conveyed therethrough byevaporation, an outlet or leg portion 18 located below heat exchangeportion 16 for receiving the concentrated or partially concentratedliquid along with the vapors, and a base portion 20 located below outletportion 18 for vertically supporting outer housing 12. Evaporationassembly 10 also includes a vapor circulating system 22 rigidly coupledbetween inlet portion 14 and outlet portion 18 as seen in FIG. 2, and aliquid circulating system 24 rigidly coupled to outer housing 12.

Vapor circulating system 22 circulates or conveys the vapors, usuallywater vapors, generated by the evaporation of the liquid conveyedthrough heat exchange portion 16 into the inlet liquid at a sufficientvelocity and pressure to increase the velocity of the mixture of thesevapors and the inlet liquid for impeding the precipitated particles ordeposits from adhering to the heat exchange surfaces. At highervelocities, the vapors increase the velocity of the inlet liquid tocause the inlet liquid to break up into droplets. These droplets ofliquid contact the exchange surfaces with sufficient force to remove orimpede precipitated particles or deposits, which adhere to the heatexchange surfaces.

Evaporation assembly 10 can be either a single effect system or usedtogether with a plurality of evaporation assemblies 10 for a multipleeffect system. Likewise, evaporation assembly may be either a fallingfilm type, a rising film type, or any other suitable type of evaporationassembly. However, for clarity, only a single effect falling film typeevaporation assembly will be discussed in detail.

Inlet or head portion 14 is defined by a cover 26, a first circularplate 28 and a portion of cylindrical wall 30 of outer housing 12extending between cover 26 and first plate 28. As seen in FIGS. 2 and 3,inlet portion 14 is divided into four equally sized inlet sections 31,32, 33 and 34 by baffles 36. Baffles 36 are rigidly coupled betweenfirst circular plate 28 and cover 26 for separating the inlet liquid ineach of the inlet sections 31-34 from the inlet liquid in the othersections. Inlet tubes 38, 39, 40 and 41 are rigidly coupled to cover 26for conveying inlet liquid from inlet tubes 38, 39, 40 and 41 into inletsections 31, 32, 33 and 34, respectively.

Heat exchange portion 16 is defined by a portion of cylindrical wall 30of outer housing 12 which extends between first circular plate 28 andsecond circular plate 44. A plurality of vertically extending heatexchange tubes 46 are rigidly coupled between first plate 28 and secondplate 44 for providing fluid communication between inlet portion 14 andoutlet portion 18. In particular, first plate 28 has a plurality ofopenings with each opening aligned with an upper end of one of the heatexchange tubes 46 for permitting the inlet liquid in each of thesections 31-34 to enter into heat exchange tubes 46. Second circularplate 44 has a plurality of openings with each opening being alignedwith the lower end of one of the heat exchange tubes 46 for permittingthe concentrated liquid and vapors to enter outlet portion 18.

The interior areas of heat exchange tubes 46 between first plate 28 andsecond plate 44 define an evaporation area. Accordingly, the longer theheat exchange tubes 46, the greater the evaporation area. Heat exchangetubes 46 are split into four sets of heat exchange tubes. The first setfluidly communicates with inlet section 31, the second set fluidlycommunicates with inlet section 32, the third set fluidly communicateswith inlet section 33, and the fourth set fluidly communicates withinlet section 34.

A heat medium inlet 48 is rigidly coupled to outer cylindrical wall 30for communicating a heat or hot medium, such as steam, into heatexchange portion 16 to heat all four sets of heat exchange tubes 46.Each of the four sets of heat exchange tubes 46 is heated with the samequality of thermal fluid or steam. Accordingly, when tubes 46 are heatedby the hot medium, heat is then transferred to the liquid being conveyedthrough heat exchange tubes 46 for causing the liquid to be concentratedby evaporation, and thereby produce vapors. Heat exchange portion 16also includes a non-condensible gas outlet 49 extending throughcylindrical wall 30 adjacent first plate 28 for removing thenon-condensible gas towards the condenser, and a condensed vapor outlet49a extending through cylindrical wall 30 adjacent second plate 44 forremoving the condensed vapors or condensates. It should be apparent thatheat exchange tubes 46 can be replaced with other types of heat exchangesurfaces, such as heat exchange plates.

Outlet or leg portion 18 is defined by a portion of cylindrical wall 30of outer housing 12 which extends between second circular plate 44 and athird circular plate 50. Four outlet sections 51, 52, 53, and 54 areformed by baffles 55 in outlet portion 18 for receiving the concentratedor partially concentrated liquid and vapors from heat exchange tubes 46.Each of the four sections 51-54 has a liquid outlet opening 56, 57, 58and 59, respectively, for removing the concentrated or partiallyconcentrated liquid therefrom. Sections 51-53 are fluidly coupled tocirculating system 22 by circulating tubes 70, 72 and 74, respectively,for removing vapors therefrom as discussed below. Vapors from section54, on the other hand, are discharged through a vapor outlet 60 to avapor separator 65 and then to the next effect, or to the condenser viatube 65a.

Accordingly, the following effects can utilize the vapors, usually watervapors, generated by the preceding effect as the heat medium forconcentrating the liquid in the next effect. In other words, in amultiple effect the second effect has its heat medium inlet 48 coupledto tube 65a of the first effect for utilizing the vapors generated byevaporation in the first effect for concentrating the liquid therein;the third effect has its heat medium inlet 48 coupled to tube 65a of thesecond effect for utilizing the vapors generated by evaporation in thesecond effect for concentrating the liquid therein; and so on.

Liquid circulating system 24 has four discharge tubes 61, 62, 63, and 64rigidly coupled to outlet openings 56-59, respectively, in third plate50 for removing the concentrated liquid from sections 51-54,respectively, and for conveying the concentrated fluid to the nextsection or to a collecting tank or the next effect by fluid pumps 66,67, 68 and 69. In particular, fluid pump 66 conveys the liquid fromoutlet section 51 through tube 66a and inlet tube 39 to inlet section32. Fluid pump 67 conveys the liquid from outlet section 52 through tube67a and inlet tube 40 to inlet section 33. Fluid pump 68 conveys theliquid from outlet section 53 through tube 68a and inlet tube 41 toinlet section 34. Fluid pump 69 conveys the liquid from outlet section54 through tube 69a to a collecting tank or the next effect.

As seen in FIGS. 2 and 3, vapor circulating system 22 includes threecirculating tubes 70, 72 and 74 for circulating or conveying the vaporsfrom the outlet section of one set of heat exchange tubes 46 to theinlet section of another set of heat exchange tubes 46. Whilecirculating tubes 70, 72 and 74 are illustrated as being located withinhousing 12, it will be apparent that the circulating tubes can belocated externally of housing 12.

First circulating tube 70 extends from first outlet section 51 of outletportion 18 to second inlet section 32 of inlet portion 14 for conveyingthe vapors from first outlet section 51 to second inlet section 32. Thevapors are conveyed at a sufficient velocity and pressure to impede theprecipitated particles or deposits from adhering to the heat exchangesurfaces of heat exchange tubes 46. At higher velocities, the circulatedvapors break the liquid up into liquid droplets which act as a hammer orscraper against the heat exchange surfaces of heat exchange tubes 46 forcontinuously removing precipitated particles deposited thereon. Inparticular, first circulating tube 70 has its bottom end rigidly coupledto opening 76 in third plate 50, and its upper end rigidly coupled toopening 78 in baffle 36 for fluidly communicating vapors from outletsection 51 to inlet section 32.

Second circulating tube 72 fluidly communicates second outlet section 52with third inlet section 33 for conveying vapors therethrough. Inparticular, second circulating tube 72 has its bottom end rigidlycoupled to opening 80 in third plate 50, and its upper end rigidlycoupled to opening 82 in baffle 36 for fluidly communicating vapors fromoutlet section 52 to inlet section 33.

Third circulating tube 74 fluidly communicates third outlet section 53with fourth inlet section 34 for conveying vapors therethrough. Inparticular, third circulating tube 74 has its bottom end rigidly coupledto opening 83 in third plate 50, and its upper end rigidly coupled toopening 84 in baffle 36 for fluidly communicating vapors from outletsection 53 to inlet section 34.

While evaporation assembly 10 has been illustrated with four heatexchange sections, it will be apparent that the evaporation assembly canhave fewer or more heat exchange sections, in any of a variety ofarrangements or alignments. Moreover, while evaporation assembly 10 hasbeen illustrated with heat exchange sections of equal size and number oftubes of the same diameter, it will be apparent that the evaporationassembly can be constructed with each of the heat exchange sectionsvarying in size, number of tubes, materials of the heat exchangesurfaces, the shape of the heat exchange surfaces and other aspects.

OPERATION

Referring to FIGS. 1 and 2, initially, liquid from tube 37 entersevaporation assembly 10 through inlet tube 38 into inlet section 31 ofinlet portion 14. The liquid then enters a first set of heat exchangetubes 46 communicating with inlet section 31 and begins to evaporate,thereby generating water vapors and becoming more concentrated. Inparticular, the liquid is evaporated and concentrated by the heat mediumcirculating in heat exchange portion 16, which heats heat exchange tubes46 and then the liquid being conveyed through heat exchange tubes 46.Next, the liquid exits the first set of heat exchange tubes 46 intooutlet section 51, where the vapors and partially concentrated liquidare separated.

The vapors from outlet section 51 are forced or thrusted upwardlythrough first circulating tube 70 and into inlet section 32 due to thedifferential of absolute pressure existing between inlet section 31 andinlet section 32. The partially concentrated liquid from outlet section51 is also conveyed into inlet section 32 via discharge tube 61, pump 66and inlet tube 39. The flow of partially concentrated liquid from outletsection 51 to inlet section 32 is automatically controlled by a levelcontrol valve 89, which maintains a constant level of liquid inside theoutlet section 51. The circulated vapors mix with the partiallyconcentrated liquid in inlet section 32, and then are conveyed throughthe second set of heat exchange tubes 46 at a sufficient velocity andpressure to increase the velocity of the partially concentrated liquidfor impeding precipitated particles or deposits from adhering orsticking to the heat exchange surfaces. In particular, the mixture ofpartially concentrated liquid and vapors are conveyed through the secondset of heat exchange tubes 46 communicating with inlet section 32 andoutlet section 52 to further concentrate the liquid by evaporation, andthus generate additional vapors. Also at higher velocities, thecirculated vapors break the liquid up into liquid droplets which act asscrapers to remove any deposits adhering to the heat exchange surfacesof heat exchange tubes 46. The partially concentrated liquid and thevapors generated from the first and second sets of heat exchange tubes46 exit into outlet section 52, where the vapors and partiallyconcentrated liquid are separated.

The vapors from outlet section 52 are forced or thrusted upwardlythrough second circulating tube 72 into inlet section 33 due to thedifferential of absolute pressure existing between inlet section 32 andinlet section 33. The partially concentrated liquid from outlet section52 is also conveyed into inlet section 33 via discharge tube 62, pump 67and inlet tube 40. The flow of partially concentrated liquid from outletsection 52 to inlet section 33 is automatically controlled by a levelcontrol valve 90, which maintains a constant level of liquid inside theoutlet section 52. The circulated vapors mix with the partiallyconcentrated liquid in inlet section 33, and then are conveyed throughthe third set of heat exchange tubes 46 at a sufficient velocity andpressure to increase the velocity of the partially concentrated liquidfor impeding precipitated particles or deposits from adhering orsticking to the heat exchange surfaces. In particular, the mixture ofthe partially concentrated liquid and the vapors are conveyed throughthe third set of heat exchange tubes 46 communicating with inlet section33 and outlet section 53 to further concentrate the liquid byevaporation, and thus generate additional vapors. The third set of heatexchange tubes 46 are maintained substantially free from deposits due tothe increased velocity of the liquid by the circulated vapors asdiscussed above. The partially concentrated liquid and the vaporsgenerated from the first, second and third sets of heat exchange tubes46 exit into outlet section 53, where the vapors and partiallyconcentrated liquid are separated.

Next, the vapors from outlet section 53 are forced or thrusted upwardlythrough third circulating tube 74 into inlet section 34 due to thedifferential of absolute pressure existing between inlet section 33 andinlet section 34. The partially concentrated liquid from outlet section53 is also conveyed into inlet section 34 via discharge tube 63, pump 68and inlet tube 41. The flow of partially concentrated liquid from outletsection 53 to inlet section 34 is automatically controlled by a levelcontrol valve 91, which maintains a constant level of liquid insideoutlet section 53. The circulated vapors mix with the partiallyconcentrated liquid in inlet section 34, and then are conveyed throughthe fourth set of heat exchange tubes 46 at sufficient velocity andpressure to increase the velocity of the partially concentrated liquidfor impeding precipitated particles or deposits from adhering orsticking to the heat exchange surfaces. In particular, the mixture ofpartially concentrated liquid and vapors are conveyed through the fourthset of heat exchange tubes 46 communicating with inlet section 34 andoutlet section 54 to further concentrate the liquid by evaporation, andthus generate additional vapors. The fourth set of heat exchange tubes46 are maintained substantially free from deposits due to the increasedvelocity of the liquid by the circulated vapors as discussed above. Theconcentrated liquid and the vapors generated from the first, second,third and fourth sets of heat exchange tubes 46 exit into outlet section54, where the vapors and concentrated liquid are separated.

The total vapors generated by the four sections of heat exchange tubes46 now exit evaporation assembly 10 through vapor outlet 60 to vaporseparator 65, and then to the next effect or to the condenser. Thevapors from vapor separator 65 are forced or thrusted to the next effector to the condenser due to the differential of absolute pressureexisting between vapor separator 65 and the next effect or condenser.The concentrated liquid is then conveyed to the next effect or operationvia discharge tube 64 and pump 69. The flow of concentrated liquid fromoutlet section 54 is automatically controlled by a level control valve92, which maintains a constant level of liquid inside outlet section 54.

SECOND EMBODIMENT OF FIG. 4

As seen in FIG. 4, a second embodiment of an evaporation assembly 110 isillustrated in accordance with the present invention. Evaporationassembly 110 is substantially identical to evaporation assembly 10,except that vapor circulating system 22 has been replaced with vaporcirculating system 122, liquid circulating system 24 has been replacedwith liquid circulating system 124, liquid inlet tubes 38-41 have beenreplaced with a single inlet tube 138, and baffles 36 and 56 have beenremoved. Accordingly, evaporation assembly 110 will not be discussed indetail.

Evaporation assembly 110 includes an outer housing 112 with an inletportion 114 at its upper end for receiving inlet liquid to beconcentrated and recycled vapors, a heat exchange portion 116 belowinlet portion 114 for concentrating the liquid being conveyed throughheat exchange tubes 146 by evaporation, an outlet portion 118 forreceiving the concentrated or partially concentrated liquid along withthe vapors, and a base portion 120 located below outlet portion 118.Evaporation assembly 110 also includes a vapor circulating system 122and a liquid circulating system 124.

Vapor circulating system 122 utilizes a compressor or booster 180 forcirculating the vapors generated by the heat exchange portion 116 at adesired velocity. Booster 180 is coupled in fluid communication betweeninlet portion 114 and outlet portion 118 via outlet tube 160, a vaporseparator 154 and circulating tubes 182 and 184. Circulating system 122recirculates the vapor generated by heat exchange portion 116 back intoinlet portion 114 for increasing the velocity of the liquid beingconveyed through heat exchange tubes 146 to a velocity sufficient toimpede particles or deposits from adhering to the heat exchange surfacesof heat exchange tubes 146.

Circulating tube 182 can be provided with an automatic or manual valve190 for controlling the flow rate of vapors into booster 180. Valves,such as valve 190, are conventional, and thus, valve 190 will not bediscussed herein.

Liquid circulating system 124 includes a pump 166 coupled to outlet tube161 and a circulating tube 188 coupled between pump 166 and inlet tube138 for recycling partially concentrated liquid back through heatexchange portion 116. Liquid circulating system 124 could be eliminated,since evaporation assembly 110 can be operated without recycling thepartially concentrated liquid.

In operation of evaporation assembly 110, the liquid to be evaporated orconcentrated first enters inlet portion 114, either alone or mixed withrecycled, partially or totally concentrated liquid, through inlet tube138. The liquid then enters heat exchange portion 116 via heat exchangetubes 146. While in heat exchange portion 116, the liquid isconcentrated by the heat transferred by the thermal fluid enteringhousing 112 through heat medium inlet 148, and thereby heating tubes146. The non-condensible gas of the thermal fluid is removed from heatexchange portion 116 through the outlet pipe 149 towards the vacuumstation or to the atmosphere. The condensed vapors or condensates of thethermal fluid are removed from heat exchange portion 116 through outletpipe 149a. Next, the fully or partially concentrated liquid exits tubes146 and enters outlet portion 118, where the vapors are separated fromthe liquid. The liquid is then regulated either manually orautomatically to the desired flow rate by valve 196 and then conveyedback to inlet 138 via liquid circulating system 124 and liquidrecirculating tube 188. The remaining portion of the liquid is conveyedvia liquid recirculating system 124 to the next effect or to the nextoperation via outlet tube 169. A level control valve 192 in outlet tube169 maintains a constant level of liquid inside the outlet section 118.The vapors, on the other hand, are conveyed to vapor separator 165 viatube 160. The vapors are then regulated either manually or automaticallyto the desired flow rate by valve 190 and then recirculated back intoinlet portion 114 via vapor recirculating system 122. The remainingvapors are conveyed to the next effect or to a condenser via pipe 189.

THIRD EMBODIMENT OF FIG. 5

As seen in FIG. 5, a third embodiment of an evaporation assembly 210 isillustrated in accordance with the present invention. Evaporationassembly 210 is substantially identical to evaporation assembly 10,except that liquid circulating system 24 has been replaced with modifiedliquid circulating system 224. Accordingly, evaporation assembly 210will not be discussed or illustrated in detail.

Referring to FIG. 5, an evaporation assembly 210 includes an outerhousing 212 with an inlet or head portion 214 at its upper end forreceiving inlet liquid to be concentrated, a heat exchange portion 216below inlet portion 214 for concentrating the liquid being conveyedtherethrough by evaporation, an outlet or leg portion 218 located belowheat exchange portion 216 for receiving the concentrated or partiallyconcentrated liquid along with the vapors, and a base portion 220located below outlet portion 218 for vertically supporting outer housing212. Evaporation assembly 210 also includes a vapor circulating system222 rigidly coupled between inlet portion 214 and outlet portion 218,and a liquid circulating system 224 rigidly coupled to outer housing212.

Vapor circulating system 222 includes three circulating tubes 270, 272and 274 for circulating or conveying the vapors from the outlet sectionof one set of heat exchange tubes 246 to the inlet section of anotherset of heat exchange tubes 246.

Liquid circulating system 224 has four discharge tubes 261, 262, 263,and 264 rigidly coupled to outlet openings 256-259, respectively, inthird plate 250 for removing the concentrated liquid from theirrespective outlet sections, and for conveying the concentrated fluid tothe next section or to the same section or to a collecting tank or thenext effect by fluid pumps 266, 267, 268 and 269. In particular, fluidpump 266 conveys a first part of the liquid from the first outletsection through tube 266a to inlet tube 239 of the second inlet section,and a second part of the liquid from the first outlet section throughtube 285 to inlet tube 238 of the first inlet section. Fluid pump 267conveys a first part of the liquid from the second outlet sectionthrough tube 267a to inlet tube 240 of the third inlet section and, asecond part of the liquid from the second outlet section through tube286 to inlet tube 239 of the second inlet section. Fluid pump 268conveys a first part of the liquid from the third outlet section throughtube 268a to inlet tube 241 of the fourth inlet section, and a secondpart of the liquid from the third outlet section through tube 287 toinlet tube 240 of the third inlet section. Fluid pump 269 conveys afirst part of the liquid from the fourth outlet section through tube269a to a collecting tank or the next effect, and a second part of theliquid from the fourth outlet section through tube 288 to inlet tube 241of the fourth inlet section.

The liquid flow through tubes 266a, 267a, 268a and 269a is regulated tothe desired flow by valves 289, 290, 291 and 292, respectively, whichmaintain a constant liquid level inside the outlet portions ofevaporation assembly 210. The liquid flow through tubes 285, 286, 287and 288 is regulated to the desired flow rate by valves 293, 294, 295and 296, respectively. Valves 289-296 can be either manual or automaticcontrol valves.

In operation, evaporation assembly 210 operates in substantially thesame manner as evaporation assembly 10, except that a portion of liquidmay be recycled back to the same inlet section via tubes 285-288 andcontrol valves 293-296.

While only three embodiments have been chosen to illustrate theinvention, it will be understood by those skilled in the art thatvarious changes and modifications can be made therein without departingfrom the scope of the invention as defined in the amended claims.

What is claimed is:
 1. An evaporation assembly for concentratingliquids, comprising:means for defining an evaporation area; liquid inletmeans, coupled to said evaporation area adjacent one end thereof, forconveying liquid to be concentrated into said evaporation area; liquidand vapor outlet means, coupled to said evaporation area adjacent anopposite end of said evaporation area, for removing and separatingconcentrated liquid and vapors from said evaporation area; heatingmeans, positioned adjacent said evaporating area, for heating liquidconveyed through said evaporation area; and vapor circulating means,coupled to said liquid and vapor outlet means and said liquid inletmeans, for conveying vapors from said liquid and vapor outlet means tosaid liquid inlet means and for mixing vapors from said outlet meanswith liquid to increase velocity of the mixture of liquid and vaporsconveyed through said evaporation area.
 2. An evaporation assemblyaccording to claim 1, whereinsaid evaporation area includes a first setof heat exchange tubes for conveying the liquid to be concentratedbetween a first section of said liquid inlet means and a first sectionof said liquid and vapor outlet means.
 3. An evaporation assemblyaccording to claim 2, whereinsaid circulating means includes means forboosting the velocity of said vapors.
 4. An evaporation assemblyaccording to claim 2, whereinsaid evaporation area further includes asecond set of heat exchange tubes for conveying liquid partiallyconcentrated in said first set of heat exchange tubes between a secondsection of said liquid inlet means and a second section of said liquidand vapor outlet means, and said circulating means includes a firstcirculating tube fluidly communicating said first section of said liquidand vapor outlet means with said second section of said liquid inletmeans.
 5. An evaporation assembly according to claim 4, whereinsaidfirst and second sets of heat exchange tubes are located in a housinghaving a heat medium inlet; and said heating means conveys a hot fluidthrough said heat medium inlet and circulates said hot fluid about saidfirst and second sets of heat exchange tubes.
 6. An evaporation assemblyaccording to claim 5, whereinsaid first and second set of heat exchangetubes extend vertically within said housing.
 7. An evaporation assemblyaccording to claim 5, whereinsaid first circulating tube extends withinsaid housing.
 8. An evaporation assembly according to claim 4,whereinsaid evaporation area further includes a third set of heatexchange tubes for conveying liquid partially concentrated in saidsecond set of heat exchange tubes between a third section of said liquidinlet means and a third section of said liquid and vapor outlet means,and said circulating means includes a second circulating tube fluidlycommunicating said second section of said liquid and vapor outlet meanswith said third section of said liquid inlet means.
 9. An evaporationassembly according to claim 8, whereinsaid evaporation area furtherincludes a fourth set of heat exchange tubes for conveying liquidpartially concentrated in said third set of heat exchange tubes betweena fourth section of said liquid inlet means and a fourth section of saidliquid and vapor outlet means, and said circulating means includes athird recirculating tube fluidly communicating said third section ofsaid liquid and vapor outlet means with said fourth section of saidliquid inlet means.
 10. An evaporation assembly according to claim 9,whereinsaid first, second, third and fourth sets of heat exchange tubesare located in a single housing having a heat medium inlet; and saidheating means conveys a hot fluid through said heat medium inlet andcirculates said hot fluid about each of said first, second, third andfourth sets of heat exchange tubes.
 11. An evaporation assemblyaccording to claim 1, further comprisingliquid circulating means forfluidly coupling said outlet means and said inlet means together forrecycling a portion of the concentrated liquid.